JP2009247936A - Method of inline-cleaning immersion type membrane-separation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an method of inline-cleaning an immersion type membrane separation device, capable of cleaning the surface of a separation-membrane of a separation-membrane module, without causing a significant decrease in the activity of a microorganism. <P>SOLUTION: The method of inline-cleaning an immersion type membrane-separation device 10 involving injecting a sodium hypochlorite solution into the filtrated water side of a separation-membrane module 11 that is immersed in a reaction tank 30 for treating water to be treated by activated sludge and filtrates the water to be treated, is characterized by determining the following B and/or the following C so that the amount of injected sodium hypochlorite per m<SP>3</SP>of the volume of the reaction tank 30 calculated from equation (1) indicated below becomes 100 g/m<SP>3</SP>or lower. Equation (1) is A×B×C÷D, wherein A represents the surface area (m<SP>2</SP>) of the membrane of the separation-membrane module to be cleaned, B represents the injected amount of sodium hypochlorite per m<SP>2</SP>of the surface area of the membrane of the separation-membrane module to be cleaned (L/m<SP>2</SP>), C represents the concentration of sodium hypochlorite in the sodium hypochlorite solution (g/L), and D represents the volume of the reaction tank 30 (m<SP>3</SP>). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an in-line cleaning method for a submerged membrane separation apparatus provided with a separation membrane module that is immersed in a reaction tank that stores the water to be treated and that filters the water to be treated.

  Conventionally, in order to filter the water to be treated including activated sludge and agglomerated sludge, a submerged membrane separation apparatus in which a separation membrane module for filtering the water to be treated is immersed in the water to be treated stored in a reaction tank. It is used. The submerged membrane separator is compact in equipment, the treated water obtained is clear, the concentration tank is unnecessary, and the activated sludge is kept at a high concentration in the reaction tank, so that high treatment efficiency can be obtained. It is an excellent technology with many merits.

  The submerged membrane separation apparatus is generally composed of a casing having an open top and bottom, a separation membrane module supported by the casing, an air diffuser provided below the separation membrane module, and a reaction tank in which these are immersed. Has been. The separation membrane module is connected to a filtrate water pipe for extracting filtrate from the separation membrane module, and the filtrate obtained by the separation membrane module flows through the filtrate water pipe and is led out of the separation membrane module.

  The aeration means supplies aerated air to the water to be treated in the reaction tank. By this aerated air, oxygen is supplied to the activated sludge treatment, and an air lift upflow occurs in the water to be treated. This air lift upward flow applies a shearing force to the separation membrane surface of the separation membrane module and suppresses sludge accumulation on the separation membrane surface of the separation membrane module, thereby suppressing clogging of the separation membrane (air scrubbing cleaning) ).

  By the way, sludge that cannot be removed by the air lift upward flow is gradually deposited on the surface of the separation membrane module as the operation time elapses. Therefore, for example, as described in Patent Documents 1 and 2, in-line cleaning is performed in which a chemical solution for cleaning flows through the filtered water pipe in the reverse direction of the flow of filtered water and is injected into the separation membrane module. By this in-line cleaning, the sludge on the separation membrane surface of the separation membrane module is removed. As the chemical solution, when the sludge deposited on the separation membrane is due to organic matter, an oxidizing agent such as sodium hypochlorite solution is used. When the sludge is due to inorganic matter, oxalic acid, citric acid, An acid solution such as hydrochloric acid is used.

In the in-line cleaning, when a sodium hypochlorite solution is used, the sterilizing power of the sodium hypochlorite solution may reduce the microbial activity in the reaction tank. However, in the conventional submerged membrane separator, the amount of injection of sodium hypochlorite with respect to the capacity of 1 m ³ of the reaction tank was such that a separation membrane of several m ² per 1 m ³ of the capacity of the reaction tank was filled. However, the microbial activity did not decrease as much as feared.
Japanese Patent No. 3290556 JP 11-33372 A

However, when performing in-line cleaning using a sodium hypochlorite solution on a separation membrane module that is immersed in a reaction vessel at high density, the membrane area to be cleaned is large, so a large amount of hypochlorous acid is required. A sodium solution had to be injected. As a result, the amount of sodium hypochlorite with respect to the volume of 1 m ³ of the reaction vessel increased, and there was a risk of causing a significant decrease in microbial activity. In particular, hollow fiber membrane modules that have been developed in recent years can have a high packing density of several tens of m ² per 1 m ³ of capacity of the reaction tank, and in such a case, the decrease in microbial activity is more remarkable. there were.
The present invention has been made in view of the above circumstances, and an object thereof is an in-line cleaning method for a submerged membrane separation apparatus capable of cleaning the separation membrane surface of a separation membrane module without causing a significant decrease in microbial activity. .

As a result of intensive studies, the inventors have found that the activity of microorganisms is greatly reduced under conditions exceeding 100 g / m ³ as the amount of sodium hypochlorite injected with respect to a volume of 1 m ³ of the reaction vessel, The present invention has been completed. That is, in order to achieve the above object, the present invention employs the following configuration.
[1] Submerged membrane separation in which the water to be treated is immersed in a reaction tank for treating activated sludge, and a sodium hypochlorite solution is injected and washed on the filtrate side of the separation membrane module for filtering the water to be treated An in-line cleaning method for an apparatus,
The following B and / or C is determined so that the amount of sodium hypochlorite injected per 1 m ^{3 of} reaction tank volume calculated from the following formula (1) is 100 g / m ³ or less. An in-line cleaning method for a submerged membrane separator.
Sodium hypochlorite injection amount per 1 m ^{3 of} reaction tank capacity (g / m ³ )
= A × B × C ÷ D (1)
A: Membrane area (m ² ) of the separation membrane module to be cleaned
B: Sodium hypochlorite solution injection amount (L / m ² ) per 1 m ² membrane area of the separation membrane module to be cleaned
C: Sodium hypochlorite solution concentration (g / L)
D: Capacity of reaction tank (m ³ )

[2] A: Membrane area (m ² ) / D of separation membrane module to be cleaned / D: The packing density of the separation membrane represented by the capacity (m ³ ) of the reaction vessel is 10 m ² / m ³ or more. The in-line cleaning method for a submerged membrane separator according to [1], which is characterized in that
[3] The in-line cleaning method for a submerged membrane separator according to [1] or [2], wherein the separation membrane module is a hollow fiber membrane module.
[4] In any one of [1] to [3], the plurality of separation membrane modules are subjected to in-line cleaning in the order of every two or more separation membrane module groups including one or more separation membrane modules. In-line cleaning method for submerged membrane separators.

  According to the in-line cleaning method of the submerged membrane separation apparatus of the present invention, the separation membrane surface of the separation membrane module can be cleaned without causing a significant decrease in microbial activity.

Hereinafter, an embodiment of an in-line cleaning method for a submerged membrane separation apparatus according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, the submerged membrane separation apparatus 10 includes a box-shaped casing 12 having an open top and bottom, a separation membrane module 11 supported by the casing 12, and a dispersion disposed below the separation membrane module 11. The gas means 14 and a reaction tank 30 in which these are immersed in the water to be treated are roughly configured. In addition, to the reaction tank 30, a to-be-treated water supply pipe 40 that supplies the to-be-treated water to the reaction tank 30 is connected. The treated water feed pipe 40 is provided with a treated water feed pump 41.

  A blower 43 that supplies air (aerated air) to the air diffuser 14 is connected to the air diffuser 14 through an air air supply pipe 42. The separation membrane module 11 is connected to a filtrate water pipe 44 for leading filtrate from the separation membrane module 11. A filtrate water suction pump 45 that applies a suction pressure (negative pressure) to the separation membrane module 11 and a first automatic valve 46 are installed in the filtrate water pipe 44. Further, a chemical liquid pipe 49 is connected to the filtrate water pipe 44 between the first automatic valve 46 and the separation membrane module 11 to connect the chemical liquid storage tank 48 for storing the chemical liquid and the filtrate water pipe 44. . The chemical liquid pipe 49 is provided with a chemical liquid supply pump 50 for supplying a chemical liquid and a second automatic valve 51.

  The separation membrane module 11 communicates with one or a plurality of separation membranes, the inside of the separation membrane (filtrated water side), a recovery member that collects filtrate water obtained by the separation membrane, and the separation membrane is fixed in the casing And a fixing member. A filtered water pipe 44 is connected to the recovery member, and the filtered water flows through the filtered water pipe 44 and is led out of the separation membrane module 11.

Examples of the separation membrane include a reverse osmosis membrane (RO membrane, NF membrane), a microfiltration membrane (MF membrane), and an ultrafiltration membrane (UF membrane).
Examples of the material for the separation membrane include polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysulfone (PS), and polyethylene (PE).
The form of the separation membrane is a hollow fiber membrane having a hollow cylindrical thread shape with an outer diameter of about 0.5 to 30 mm, and a tubular tube having a hollow cylindrical shape with an outer diameter of about 30 to 100 mm that is thicker than the hollow fiber membrane. Examples of the membrane include a flat membrane having a sheet shape. Among these, a hollow fiber membrane is preferable. The hollow fiber membrane module including the hollow fiber membrane has a separation membrane packing density per 1 m ^{3 of the} reaction tank (a value obtained by dividing the membrane area of the separation membrane module by the capacity of the reaction tank) of 10 m ² / m ^3. It is also possible to make the above, and the effect of the in-line cleaning method of the present invention is remarkably exhibited.

The casing 12 is a box-shaped structure that is open at the top and bottom, supports the separation membrane module 11 in the box, and is generated in the water to be treated by the release of air from the air diffuser 14 during operation of the apparatus. It is provided to restrict the flow path of the air lift upflow. The casing 12 is provided between the upper end of the casing 12 and the surface of the water to be treated, and between the lower end of the casing 12 and the bottom surface of the reaction tank 30 so as not to hinder the flow of the air lift upward flow caused by aeration during operation. It is immersed and installed with an arbitrary interval between them.
The air diffuser 14 is disposed below the separation membrane module 11, and promotes microbial treatment in the water to be treated by releasing air (aerated air), and generates an air lift upward flow in the water to be treated. The surface of the separation membrane is provided for air scrubbing cleaning.

  The reaction tank 30 is a tank that performs microbial treatment of water to be treated with activated sludge. The reaction tank 30 is made of concrete, steel, or the like, and is provided indoors or outdoors. The reaction tank 30 holds activated sludge having a sludge concentration of about 5000 to 20000 mg / L.

Next, the operation state of the submerged membrane separation apparatus 10 will be described with reference to FIG.
During operation of the submerged membrane separation apparatus 10, the first automatic valve 46 is opened, the second automatic valve 51 is closed, and the filtered water suction pump 45 is activated. Thereby, the suction pressure (negative pressure) by the filtrate water suction pump 45 is applied to the separation membrane module 11 through the filtrate water pipe 44. The filtrate obtained by filtering with the separation membrane module 11 is led out of the separation membrane module 11 through the filtrate water pipe 44. Since the filtered water led out of the separation membrane module 11 has a very good water quality, it can be reused. The flow rate of the filtered water sucked by the filtered water suction pump 45 is preferably set so that the flux with respect to the membrane area is 0.1 to 1.0 m / d.

When the submerged membrane separator 10 is operated, air (aerated air) is also supplied into the reaction tank 30 in parallel with the suction pressure by the filtered water suction pump 45. Air is supplied from the blower 43 to the air diffuser 14 through the air supply pipe 42 and is discharged from the air diffuser 14 into the water to be treated. As the air released into the water to be treated rises toward the surface of the water to be treated, an air lift upward flow is generated in the portion surrounded by the casing 12. And when the to-be-processed water which rises by an air lift upward flow passes the circumference | surroundings of the separation membrane module 11, a shearing force is added to the separation membrane surface of the separation membrane module 11. FIG.
Thus, by supplying aeration air into the water to be treated, oxygen necessary for microbial treatment is supplied, and air scrubbing cleaning of the separation membrane surface of the separation membrane module 11 is performed. By this air scrubbing cleaning, accumulation of sludge on the separation membrane surface of the separation membrane module 11 is suppressed.

  The water to be treated that has risen to the vicinity of the water surface by the air lift ascending flow passes between the upper end of the casing 12 and the surface of the water to be treated, and then flows downward toward the bottom surface of the reaction tank 30. And the to-be-processed water which fell to the bottom face vicinity of the reaction tank 30 passes between the lower end of the casing 12 and the bottom face of the reaction tank 30, and rises again by an air lift upward flow. As described above, the water to be treated in the reaction tank 30 is agitated, so that the microbial treatment is promoted and the air scrubbing cleaning is efficiently performed.

Next, in-line cleaning of the submerged membrane separation apparatus 10 will be described with reference to FIG.
By the air scrubbing cleaning, accumulation of sludge on the separation membrane surface of the separation membrane module 11 is suppressed. However, when the operation of the submerged membrane separation apparatus 10 is continued for a long period of time, sludge is gradually deposited on the surface of the separation membrane of the separation membrane module 11, and the separation membrane is likely to be clogged. Therefore, in addition to air scrubbing cleaning, sludge removal by injection of a chemical solution into the separation membrane module 11, that is, in-line cleaning is performed.

  In the in-line cleaning, the first automatic valve 46 is closed to stop the filtered water suction pump 45, and the second automatic valve 51 is opened to start the chemical solution supply pump 50. Thereby, the chemical solution stored in the chemical solution storage tank 48 is pressurized and injected into the separation membrane module 11 through the chemical solution pipe 49 and the filtrate water pipe 44 to fill the filtrate side (inside the separation membrane) of the separation membrane module 11. The filtered water is replaced with a chemical solution, and is held for a certain period of time in a state where the chemical solution is leached to the treated water side of the separation membrane module 11, and the sludge accumulated on the separation membrane surface of the separation membrane module 11 is decomposed and removed.

  A sodium hypochlorite solution is used as the chemical solution. By injecting the sodium hypochlorite solution into the separation membrane module 11, the organic sludge deposited on the separation membrane surface of the separation membrane module 11 is decomposed by the oxidizing power of the sodium hypochlorite solution and separated. It is removed from the film surface.

Here, in the in-line cleaning method of the submerged membrane separation apparatus of the present invention, the amount of sodium hypochlorite injected per 1 m ^{3 of} reaction tank calculated from the following equation (1) is 100 g / m ³ or less, preferably The following “B: sodium hypochlorite solution injection amount per 1 m ² of membrane area to be cleaned” and / or “C: sodium hypochlorite solution concentration” below is determined so as to be 50 g / m ³ or less. .
Sodium hypochlorite injection amount per 1 m ^{3 of} reaction tank capacity (g / m ³ )
= A × B × C ÷ D (1)
A: Membrane area (m ² ) of the separation membrane module to be cleaned
B: Sodium hypochlorite solution injection amount (L / m ² ) per 1 m ² membrane area of the separation membrane module to be cleaned
C: Sodium hypochlorite solution concentration (g / L)
D: Capacity of reaction tank (m ³ )

When the amount of sodium hypochlorite injected per 1 m ^{3 of the} reaction vessel calculated from the above equation (1) exceeds 100 g / m ³ , the microbial activity is significantly reduced.
By determining “B” and / or “C” so that the sodium hypochlorite injection amount per 1 m ^{3 of the} reaction vessel volume calculated from the above equation (1) is 50 g / m ³ or less, The decrease in microbial activity due to sodium chlorite is less likely to occur.

It exists in the packing density of the separation membrane represented by “A: membrane area (m ² ) of separation membrane module to be cleaned” / “D: reaction tank capacity (m ³ )”, that is, the reaction tank capacity is 1 m ³ . The membrane area of the separation membrane is preferably 10 m ² / m ³ or more. That is, if it is a hollow fiber membrane module having a packing density of several tens m ² / m ³ and a separation membrane module placed in a treatment tank at a high density, the microbial activity is significantly reduced. In addition, the effect of the present invention that the separation membrane surface of the separation membrane module can be cleaned can be exhibited more remarkably.

"B: sodium hypochlorite solution injection amount of film per area 1 m ² to be cleaned in the separation membrane module" may preferably be ^{1~10L / m 2, 2~5L / m} 2 is more preferable. If “B” is 1 L / m ² or more, the filtered water in the separation membrane module 11 is replaced, and the chemical solution is leached on the separation membrane surface of the separation membrane module 11 to sufficiently remove the sludge on the separation membrane surface. Can be removed. If “B” is 10 L / m ² or less, the chemical solution from the separation membrane surface of the hollow fiber membrane module 11 is not leached more than necessary, and the decrease in microbial activity can be suppressed.

  “C: Sodium hypochlorite solution concentration” is preferably 0.5 to 10 g / L, and more preferably 0.5 to 6 g / L. If “C” is 0.5 g / L or more, it is easy to obtain a sufficient film cleaning effect. If “C” is 10 g / L or less, a decrease in microbial activity due to a sodium hypochlorite solution leached into the water to be treated can be suppressed, and a hollow fiber membrane module using a high concentration sodium hypochlorite solution 11 (promotion of deterioration of the separation membrane) hardly occurs.

In-line cleaning may be performed periodically. A suction pressure gauge is provided upstream of the filtered water suction pump 45 in the filtered water pipe 44, and an increase in suction pressure detected by the suction pressure gauge is used as a guide. You may implement suitably.
The retention time of the sodium hypochlorite solution in the separation membrane module 11 is preferably 1 to 3 hours. When the holding time is 1 hour or longer, the sludge can be sufficiently decomposed by the leaching of the sodium hypochlorite solution. If the holding time is within 3 hours, in-line cleaning can be performed without taking more time than necessary.

The sodium hypochlorite solution may contain other chemical components such as sodium hydroxide.
In addition to in-line washing with a sodium hypochlorite solution, in-line washing with oxalic acid, citric acid, hydrochloric acid, etc. may be performed for the purpose of dissolving and removing inorganic substances solidified on the surface of the separation membrane.

As described above, in the in-line cleaning method of the submerged membrane separation apparatus of the present invention, the amount of sodium hypochlorite injected per 1 m ^{3 of the} reaction vessel calculated from the above equation (1) is 100 g / m ³ or less. Thus, the activity is determined by determining “B: sodium hypochlorite solution injection amount per 1 m ² of membrane area of the separation membrane module to be cleaned” and / or “C: sodium hypochlorite solution concentration”. The effect on microorganisms in sludge can be reduced. As a result, the separation membrane surface of the separation membrane module can be cleaned without significantly reducing the microbial activity.

  Although the above-mentioned embodiment was the immersion type membrane separation apparatus 10 provided with one separation membrane module 11 in the reaction tank 30, the in-line cleaning method of the immersion type membrane separation apparatus of the present invention is shown in FIG. Like the submerged membrane separator 100, the plurality of separation membrane modules 11 may be subjected to in-line cleaning in the order of the plurality of separation membrane module groups 110a, 110b, 110c, and 110d.

  In this embodiment, the submerged membrane separation apparatus 100 includes eight separation membrane modules 11, a filtrate water pipe 44 connected to each separation membrane module 11, and a chemical solution pipe 49 connected to each separation membrane module 11. , And the reaction tank 300 in which these are immersed and installed. The eight separation membrane modules 11 are made into one separation membrane module group by the two separation membrane modules 11 and constitute the separation membrane module groups 110a, 110b, 110c, and 110d, and are immersed in the reaction tank 300. Has been.

Connected to the separation membrane module group 110a are a filtrate branch pipe 44a branched from the filtrate pipe 44 and a chemical branch pipe 49a branched from the chemical pipe 49. The filtered water branch pipe 44a is provided with a first automatic valve 46a, and the chemical liquid branch pipe 49a is provided with a second automatic valve 51a.
Connected to the separation membrane module group 110 b are a filtrate branch pipe 44 b branched from the filtrate pipe 44 and a chemical branch pipe 49 b branched from the chemical pipe 49. The filtered water branch pipe 44b is provided with a first automatic valve 46b, and the chemical liquid branch pipe 49b is provided with a second automatic valve 51b.
The separation membrane module group 110 c is connected to a filtrate branch pipe 44 c branched from the filtrate pipe 44 and a chemical branch pipe 49 c branched from the chemical pipe 49. The filtered water branch pipe 44c is provided with a first automatic valve 46c, and the chemical liquid branch pipe 49c is provided with a second automatic valve 51c.
Connected to the separation membrane module group 110d are a filtrate branch pipe 44d branched from the filtrate pipe 44 and a chemical branch pipe 49d branched from the chemical pipe 49. The filtered water branch pipe 44d is provided with a first automatic valve 46d, and the chemical liquid branch pipe 49d is provided with a second automatic valve 51d.

The filtered water suction pump 45 that sucks the filtered water and the chemical liquid supply pump 50 that pushes out the chemical liquid are common to the separation membrane module groups 110a, 110b, 110c, and 110d. In addition, a water to be treated water supply pipe 40 for supplying water to be treated is connected to the reaction tank 300. The treated water feed pipe 40 is provided with a treated water feed pump 41 in the reaction tank 300.
In the embodiment of FIG. 2, for convenience of explanation, an air diffuser that discharges air into the water to be treated, a blower that supplies air to the diffuser, and an air supply pipe that connects the diffuser and the blower are not illustrated. Yes.

  During operation of the submerged membrane separation apparatus 100, the first automatic valves 46a, 46b, 46c, 46d are opened, the second automatic valves 51a, 51b, 51c, 51d are closed, and the filtered water suction pump 45 is activated. Thereby, the suction pressure (negative pressure) by the filtrate suction pump 45 is applied to the separation membrane module groups 110a, 110b, 110c, and 110d through the filtrate water pipe 44 and the filtrate water branch pipes 44a, 44b, 44c, and 44d. Then, the filtrate obtained from these separation membrane module groups is led out from these separation membrane module groups through the filtrate water branch pipes 44 a, 44 b, 44 c and 44 d and the filtrate water pipe 44. In addition, during operation of the submerged membrane separator 100, in addition to the suction pressure by the filtered water suction pump 45, air is also supplied into the reaction tank 300 in the same manner as the submerged membrane separator 10 described above.

At the time of in-line cleaning, the first automatic valve 46a is closed and the second automatic valve 51a is opened. Then, the chemical solution supply pump 50 is activated to inject the sodium hypochlorite solution into the separation membrane module group 110a. Here, also in the submerged membrane separator 100, as in the submerged membrane separator 10 described above, “sodium hypochlorite injection amount per 1 m ³ capacity of the reaction vessel” calculated from the above equation (1). To be 100 g / m ³ or less, “B: sodium hypochlorite solution injection amount per 1 m ² of membrane area of the separation membrane module to be cleaned (L / m ² )” and / or “C: hypoxia "Sodium chlorate solution concentration (g / L)" is determined.
In this way, in-line cleaning is performed on the separation membrane module group 110a. During the in-line cleaning of the separation membrane module group 110a, the filtration by the separation membrane module group 110b, 110c, and 110d may be continued, so that the in-line cleaning is performed while the operation of the submerged membrane separation apparatus 100 is continued. Can be implemented.

  After the in-line cleaning for the separation membrane module group 110a, the first automatic valve 46a is opened, the second automatic valve 51a is closed, and filtration by the separation membrane module group 110a is resumed. Next, the same operation as the in-line cleaning for the separation membrane module group 110a is sequentially performed on the separation membrane module groups 110b, 110c, and 110d.

Thus, by performing in-line cleaning, “A: membrane area of separation membrane module to be cleaned” in the above-described formula (1) can be reduced. Thereby, “B: sodium hypochlorite solution injection amount per 1 m ² of membrane area of the separation membrane module to be cleaned” and / or “C: sodium hypochlorite solution concentration” can be set high, While reducing the influence on microorganisms in the activated sludge, a higher cleaning effect can be obtained.

  In order to further reduce the influence of in-line cleaning on microorganisms, it is preferable to perform in-line cleaning for each separation membrane module group at a sufficient interval and in a constant cycle. For example, the in-line cleaning of the separation membrane module group 110a is performed, the in-line cleaning of the separation membrane module group 110b is performed two weeks later, the in-line cleaning of the separation membrane module group 110c is performed two weeks later, and two weeks later The separation membrane module group 110d is subjected to in-line cleaning, and two weeks later, the separation membrane module group 110a is subjected to in-line cleaning. As described above, by performing in-line cleaning at a sufficient interval with respect to each separation membrane module group (in this example, about once every two months), the surface of the separation membrane is obtained. While being maintained clean, the filtration performance can be maintained more stably, and the influence of the sodium hypochlorite on the microorganism can be sufficiently recovered, and the decrease in the microbial activity is less likely to occur.

  In the embodiment including the plurality of separation membrane modules 11 described above, one set of separation membrane module group is configured by two separation membrane modules 11, but the in-line cleaning method of the present invention is included in the separation membrane module group. The number of separation membrane modules is not particularly limited, and can be implemented. Further, in this embodiment, the four separation membrane module groups 110a to 110d are configured by the plurality of separation membrane modules 11, but the in-line cleaning method of the present invention is not particularly limited in the number of separation membrane module groups. Is possible.

  In the embodiment including the plurality of separation membrane modules 11 described above, the filtered water suction pump and the chemical solution supply pump are common to all the separation membrane modules 11, but the in-line cleaning method of the present invention uses the separation membrane module groups 110a to 110a. The present invention is also applicable to a submerged membrane separation apparatus provided with a filtered water suction pump and / or a chemical solution supply pump for each 110d.

According to the in-line cleaning method of the submerged membrane separation apparatus of the present invention, the surface of the separation membrane of the separation membrane module can be cleaned without causing a decrease in microbial activity.
Moreover, according to the in-line cleaning method of the submerged membrane separation apparatus of the present invention, in the case of the submerged membrane separation apparatus provided with a plurality of separation membrane modules, every two or more separation membrane module groups composed of one or more separation membrane modules By performing the in-line cleaning in this order, the microbial activity is less likely to decrease.

Hereinafter, the in-line cleaning method for the submerged membrane separation apparatus according to the present invention will be described in more detail with reference to examples. The abbreviations and measurement methods in the examples are as follows.
MLSS: (Mixed Liquid Suspended Solids) is an abbreviation for suspended solids (SS) concentration in treated water, that is, activated sludge concentration in treated water.
Measurement of respiration rate: The respiration rate of activated sludge was measured according to the measurement method of “Oxygen utilization rate” described in “Sewage test method (issued by Japan Sewerage Association)”.
Measurement of TOC: Total organic carbon analyzer (TOC-5000, manufactured by Shimadzu Corporation)
Was used to measure total organic carbon (TOC) in the water to be treated.
(Reference example)
The activated sludge whose MLSS was adjusted to 10 g / L was sampled in 5 liter samples. A 12% by mass sodium hypochlorite solution was added to each of the collected samples so that a predetermined sodium hypochlorite addition amount (g / m ³ ) was obtained, and each sample was stirred for 2 hours with a stirrer. Stir. Then, the respiration rate of each sample was measured, and the ratio (increase / decrease rate) of the activated sludge with sodium hypochlorite added to the respiration rate of the sample without sodium hypochlorite added was calculated. It was used as an index of activity. As a result, as shown in the graph of FIG. 3, if the amount of sodium hypochlorite added to the reaction tank volume of 1 m ³ is 100 g / m ³ or less, the decrease in the respiration rate is not so great and there is concern. It was found that there was no significant decrease in microbial activity.

Example 1
The in-line cleaning of Example 1 was performed on the immersion type membrane separation apparatus 10 shown in FIG. Here, the tank capacity of the reaction tank 30 was set to 0.7 m ³ . Further, a hollow fiber membrane module was used as the separation membrane module 11, and the total membrane area was 25 m ² . That is, the packing density of the separation membrane with respect to the tank capacity was about 35.7 m ² / m ³ .

To this reaction tank 30, treated water having a TOC of 20 to 50 mg / L is supplied at a flow rate of 7 m ³ / day by a treated water feed pump, and a tank capacity of 0.7 m ³ in the reaction tank 30 is supplied to the treated water. Then, air is supplied from the lower side of the membrane module 11 by the blower 43 to aerate the treated water, the first automatic valve 46 is opened, the filtered water suction pump 45 is activated, and the submerged membrane separation device 10 Started operation. Thereby, filtrate water was continuously led out of the reaction tank 30 from the separation membrane module 11 through the filtrate water pipe 44. Moreover, the organic substance in to-be-processed water is decomposed | disassembled by the driving | operation of the immersion type membrane separator 10, and TOC (total organic carbon) reduces. Since the mass of the activated sludge in the reaction tank 30 increases with this, the activated sludge was appropriately extracted so that the sludge concentration in the reaction tank 30 would be 8000 to 10000 mg / L.

When 60 days passed from the start of operation, the suction pressure became about −20 kPa due to the accumulation of sludge on the separation membrane surface of the separation membrane module 11 (initial operation was −5 kPa). Here, in-line cleaning was performed as follows. First, the first automatic valve 46 was closed, and the filtered water suction pump 45 and the blower 43 were stopped. Then, the second automatic valve 51 is opened, the chemical cleaning pump 50 is activated, and the sodium hypochlorite solution stored in the chemical storage tank 48 flows through the chemical piping 49 and the filtrate piping 44 through the filtrate water. The injection was performed in the opposite direction over 2 hours. Here, the injection amounts of “A” and “B” were determined as shown below so that the injection amount of sodium hypochlorite with respect to the capacity of the reaction tank did not exceed 100 g / m ³ .
A: Membrane area of the separation membrane module to be cleaned = 25 m ²
B: Sodium hypochlorite solution injection amount per 1 m ² of membrane area of the separation membrane module to be cleaned = ² L / m ²
C: Sodium hypochlorite solution concentration = 0.75 g / L
D: Capacity of reaction tank = 0.7 m ³
Injection amount of sodium hypochlorite with respect to the capacity of the reaction tank (g / m ³ )
= A × B × C ÷ D = 25 × 2 × 0.75 ÷ 0.7≈70 g / m ³

  After the injection of the sodium hypochlorite solution, the second automatic valve 51 is closed, the chemical cleaning pump 50 is stopped, the first automatic valve 46 is opened, the filtered water suction pump 45 and the blower 43 are restarted, The operation of the submerged membrane separation apparatus 10 was resumed.

  Two hours after restarting the operation, the activated sludge and filtered water in the reaction tank 30 were collected, and the respiratory rate of the activated sludge and the TOC of the filtered water were measured as indicators of microbial activity. Furthermore, regarding the respiration rate, the ratio (increase / decrease rate) of the respiration rate after addition of sodium hypochlorite to the respiration rate of the activated sludge measured in advance before in-line cleaning was calculated. The results are shown in Table 1.

(Comparative Example 1)
A submerged membrane separation apparatus having the same configuration as in Example 1 was operated in the same manner as in Example 1. Then, the sodium hypochlorite solution concentration (C) was changed as described below, and inline cleaning was performed in the same manner as in Example 1 except that the sodium hypochlorite solution was injected. Respiratory activity and TOC of filtered water were measured, and the ratio of the respiration rate before in-line cleaning was calculated. The results are shown in Table 1.
A: Membrane area of the separation membrane module to be cleaned = 25 m ²
B: Sodium hypochlorite solution injection amount per 1 m ² of membrane area of the separation membrane module to be cleaned = ² L / m ²
C: Sodium hypochlorite solution concentration = 3 g / L
D: Capacity of reaction tank = 0.7 m ³
Injection amount of sodium hypochlorite with respect to the capacity of the reaction tank (g / m ³ )
= A × B × C ÷ D = 25 × 2 × 3 ÷ 0.7≈210 g / m ³

As shown in Table 1, in Example 1, a noticeable decrease in respiration rate was not observed as compared with that before in-line cleaning, and it was confirmed that no significant decrease in microbial activity occurred. In Example 1, the TOC of filtered water was 3 mg / L, which was almost unchanged compared with that before in-line cleaning. Therefore, in Example 1, the decomposition of organic matter by microorganisms in activated sludge progressed smoothly, the TOC in the treated water was not different from the normal time, and the TOC contained in the filtered water also showed the same value as before in-line washing. Inferred.
On the other hand, in Comparative Example 1, the respiration rate was significantly reduced as compared with that before in-line cleaning, and a significant decrease in microbial activity was confirmed. Moreover, in the comparative example 1, the TOC of filtered water rose to 10 mg / L. It was speculated that the increase in the TOC of filtered water in Comparative Example 1 was caused by a significant decrease in microbial activity. That is, due to a significant decrease in microbial activity, the decomposition of organic matter by microorganisms in activated sludge does not proceed smoothly, thereby slowing the decrease in TOC in the treated water, increasing the TOC in the treated water, and adding to filtered water. It was inferred that the included TOC increased.

It is a side view which shows one Embodiment of the immersion type membrane separation apparatus immersed and installed in the reaction tank. It is a top view which shows other embodiment of the immersion type membrane separation apparatus immersed and installed in the reaction tank. Activity based on the difference in the amount of sodium hypochlorite injected, with the sodium hypochlorite injection amount (g / m ³ ) per 1 m ^{3 of the} reaction tank on the X axis and the respiration rate ratio of the activated sludge on the Y axis It is a graph which shows the increase / decrease in the respiration rate of sludge.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 Submerged membrane separator 11 Separation membrane module 14 Air diffusion means 30, 300 Reaction tank 40 Water to be treated water supply pipe 41 Water to be treated water supply pump 42 Air air supply piping 43 Blower 44 Filtration water piping 45 Filtration water suction pump 46 , 46a, 46b, 46c, 46d First automatic valve 48 Chemical liquid storage tank 49 Chemical liquid piping 50 Chemical liquid supply pump 51, 51a, 51b, 51c, 51d Second automatic valve 110a, 110b, 110c, 110d Separation membrane module group

Claims (4)

Immersion type membrane separator that is immersed in a reaction tank that treats the treated water and injects a sodium hypochlorite solution into the filtration water side of the separation membrane module that filters the treated water. A cleaning method,
The following B and / or C is determined so that the amount of sodium hypochlorite injected per 1 m ^{3 of} reaction tank volume calculated from the following formula (1) is 100 g / m ³ or less. An in-line cleaning method for a submerged membrane separator.
Sodium hypochlorite injection amount per 1 m ^{3 of} reaction tank capacity (g / m ³ )
= A × B × C ÷ D (1)
A: Membrane area (m ² ) of the separation membrane module to be cleaned
B: Sodium hypochlorite solution injection amount (L / m ² ) per 1 m ² membrane area of the separation membrane module to be cleaned
C: Sodium hypochlorite solution concentration (g / L)
D: Capacity of reaction tank (m ³ ) A: The membrane area (m ² ) / D of the separation membrane module to be cleaned / D: the packing density of the separation membrane represented by the capacity (m ³ ) of the reaction vessel is 10 m ² / m ³ or more. An in-line cleaning method for a submerged membrane separation apparatus according to claim 1.   The in-line cleaning method for an immersion type membrane separation apparatus according to claim 1, wherein the separation membrane module is a hollow fiber membrane module.   The submerged membrane separation according to any one of claims 1 to 3, wherein the plurality of separation membrane modules are subjected to in-line cleaning in the order of every two or more separation membrane module groups composed of one or more separation membrane modules. In-line cleaning method for equipment.

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